throw more detailed exceptions for type not found and interface mismatches

Octokit.Tests.Conventions/Exception/InterfaceHasAdditionalMethodsException.cs

@@ -0,0 +1,25 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.Serialization;
+
+namespace Octokit.Tests.Conventions
+{
+    public class InterfaceHasAdditionalMethodsException : Exception
+    {
+        public InterfaceHasAdditionalMethodsException(Type type, IEnumerable<string> methodsMissingOnReactiveClient)
+            : base(CreateMessage(type, methodsMissingOnReactiveClient)) { }
+
+        public InterfaceHasAdditionalMethodsException(Type type, IEnumerable<string> methodsMissingOnReactiveClient, Exception innerException)
+            : base(CreateMessage(type, methodsMissingOnReactiveClient), innerException) { }
+
+        protected InterfaceHasAdditionalMethodsException(SerializationInfo info, StreamingContext context)
+            : base(info, context) { }
+
+        static string CreateMessage(Type type, IEnumerable<string> methods)
+        {
+            var methodsFormatted = String.Join("\r\n", methods.Select(m => String.Format(" - {0}", m)));
+            return String.Format("Methods found on type {0} which should be removed:\r\n{1}", type.Name, methodsFormatted);
+        }
+    }
+}